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INTERIORS

Pioneer

Both Pioneer 10 and 11 flew relatively close to Jupiter, making measurements of its gravitational field that were more precise than what would've been possible on Earth. Like all planets, Jupiter isn't perfectly spherical. As it spins on its axis, it flattens out slightly, assuming an oblate shape. The two spacecraft determined that Jupiter was 10 times more oblate than Earth. They also found that Jupiter was 1.3 times as dense as water. While these numbers were expected, the new measurements confirmed previous ones and improved the confidence scientists had in their prior Earth-based methods. Juno will map Jupiter's gravitational field with even greater precision, helping scientists determine whether Jupiter contains a solid core.